Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2000-01-18
2001-10-16
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S065000, C526S116000, C526S348200, C525S247000
Reexamination Certificate
active
06303709
ABSTRACT:
The present invention relates to a process for gas-phase polymerization of propylene by means of a fluidized bed, and to a process for initiating a gas-phase propylene polymerization process.
It is known that the &agr;-olefins such as propylene can be polymerized in the gas phase, for example in a fluidized bed, by means of an ascending gas stream containing the &agr;-olefin or &agr;-olefins to be polymerized. The gaseous mixture exiting the reactor is generally cooled and supplemented by an additional quantity of &agr;-olefins before being recycled to the reactor. The polymerization is most often carried out using a catalytic system of the Ziegler-Natta type, introduced continuously or semicontinuously into the fluidized-bed reactor.
These catalytic systems are generally obtained by combining, on the one hand, a catalytic solid comprising a compound of a transition metal belonging to Groups IVb, Vb and VIb of the Periodic Table and, on the other hand, a cocatalyst comprising an organometallic compound of a metal of Groups Ia, IIa or IIIa. Furthermore, in the case of propylene polymerization, these catalytic systems most often contain an electron-donor compound known as an external electron donor, which is used to increase the stereospecificity of the catalyst.
It is also known that a prepolymerized catalytic solid, or in other words a catalytic solid that has previously undergone a polymerization stage more generally referred to as the prepolymerization stage, can be used in the gas-phase polymerization reactor.
For example, U.S. Pat. No. 4,721,763 describes a process for gas-phase polymerization of &agr;-olefins in a fluidized-bed reactor in the presence of a catalytic solid of spheroidal morphology and narrow particle-size distribution that has been prepolymerized so as to form a prepolymer which has the form of a powder of particles whose mass-average mean diameter is between 80 and 300 &mgr;m and which contains 2×10
−3
to 10
−1
mmole of titanium per gram. According to that document, prepolymerization is performed in two stages, the first being performed in a liquid hydrocarbon and the second in suspension in the monomer or in the gas phase. Such a process, which is particularly time-consuming and complex to use, is difficult to operate profitably on the industrial scale.
In addition, document WO 88/02376 describes a process for polymerization of &agr;-olefins comprising a first stage of liquid-phase polymerization under conditions such that the weight ratio of the &agr;-olefin or &agr;-olefins to the catalytic solid is at least equal to 6000:1, the residence time is from 10 to 400 seconds and the temperature is from 20 to 100° C., preferably 40 to 80° C., and a second stage of gas-phase polymerization at a temperature of 40 to 150° C., performed in the presence of the reaction mixture obtained from the first stage. The accomplishment of this first stage leads to an increase in catalytic productivity but does not influence the stereospecificity of the catalytic system. In addition, the morphology of the polymer powders obtained is still unsatisfactory and such a process is difficult to control.
There has now been found, for gas-phase polymerization of &agr;-olefins in a fluidized bed, a process with which propylene polymers can be obtained with particularly high yield and stereospecificity and which does not exhibit such disadvantages.
To this end, the present invention relates to a continuous process for obtaining propylene polymers in the presence of a catalytic system of the Ziegler-Natta type containing a catalytic solid comprising chlorine, magnesium and titanium atoms and at least one electron-donor compound, called internal donor, a cocatalyst which is an organoaluminum compound, and optionally an electron-donor compound, called external donor, comprising the following successive stages:
(a) polymerization of propylene in liquid propylene to form from 11000 to 28000 g, per g of titanium in the catalytic solid, of a prepolymer which is a homopolymer of propylene, and
(b) gas-phase polymerization of propylene in one or more successive fluidized-bed reactors and in the presence of the prepolymer, optionally in the presence of one or more other monomers chosen from among the &agr;-olefins containing from 2 to 12 carbon atoms, to produce a propylene polymer whose fraction of particles of diameter smaller than 125 &mgr;(FP) is at most 10 wt %.
The process according to the present invention makes it possible to obtain homopolymers of propylene as well as copolymers thereof containing preferably at least 50 wt % of propylene and more particularly at least 75 wt % of propylene.
The propylene copolymers are most often chosen from among the random or block copolymers of propylene.
The comonomers are preferably ethylene and/or 1-butene.
Preferably, the polymers obtained according to the process of the invention are such that their FP is at most 6 wt %, preferably at most 2 wt %. Polymers whose FP is smaller than 0.5% are particularly advantageous. The very particularly preferred propylene polymers do not contain particles whose diameter is smaller than 125 &mgr;m.
The titanium content of the homopolymers obtained according to the process of the invention is most often at most 3×10
−5
mmol per g, this content being preferably at most 3×10
−5
mmol per g for the copolymers of propylene and ethylene, while the titanium content of terpolymers of propylene, ethylene and butene is most often at most 9×10
31 5
mmol of titanium per g of polymer.
The catalytic solids that are usable according to the invention generally contain chlorine, magnesium, titanium and at least one internal donor as main constituents. Preferably they contain at least 10 wt % of magnesium. The catalytic solids containing at least 15 wt % of magnesium are particularly well suited. The magnesium content of the catalytic solids that are usable according to the present invention is most often at most 30 wt %. Magnesium contents of at most 25 wt % being most advantageous. The catalytic solids that are usable according to the invention preferably also contain at least 1 wt % of titanium.
This titanium content is most often at most 10 wt %. Good results are obtained when this content is at most 5 wt %. In addition, these solids contain from 20 to 80 wt % of chlorine, preferably from 50 to 75 wt % of chlorine. The internal donor is most often chosen from among the ethers, the esters, the amines, the amides, the phenols, the ketones and the oxygen-containing organic compounds of silicon. The internal donors are preferably chosen from among the carboxylic esters and more particularly from among the aromatic carboxylic diesters. The esters of phthalic acids are particularly well suited, and thereamong the di-n-butyl and di-isobutyl phthalates yield particularly good results. The total quantity of the internal donor or donors is most often from 2 to 30 wt %, most often from 5 to 20 wt % of the catalytic solid.
Particularly well suited catalytic solids are those which contain from 2 to 4 wt % of titanium, from 17 to 23 wt % of magnesium, from 55 to 75 wt % of chlorine and from 8 to 19 wt % of an internal donor chosen preferably from among the di-n-butyl and di-isobutyl phthalates.
These catalytic solids can be deposited in or on organic or inorganic supports. As examples of organic supports there can be cited the preformed polymers, and of inorganic supports the oxides of silicon, aluminium, magnesium, titanium and zirconium and mixtures thereof
The catalytic solids used preferentially in the scope of the present invention have the form of particles whose mean weight-average diameter is preferably at least 5 &mgr;m, more particularly at least 10 &mgr;m and more particularly at least 20 &mgr;m.
These preferred catalytic solids are additionally such that their mean weight-average diameter is at most 150 &mgr;m, more particularly at most 100 &mgr;m.
Catalytic solids having a mean diameter of at most 50 &mgr;m being more particularly preferred.
Preferably the catalytic particle
Cheung William
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Solvay Polyolefins Europe--Belgium (Societe Anonyme)
Wilson Donald R.
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